PURPOSE: To obtain high volume efficiency in a wide rotational speed range of an engine by setting branch passages which branch and converge on the way of an intake passage, providing valves in the inlet and outlet of each of those branch passages respectively and opening closing those voltage according to the rotational speed of an engine.

CONSTITUTION: Valves V1-V4 arranged at inlets and outlets of two branch passages 16, 18 are opened and closed respectively according to a specified engine speed. Respective branch passages 16, 18 can become intake passages, and pipes which connect with the intake passages, and the distance between the connecting position to the intake passages and an engine (surge tank) 12 changes. As a result, six kinds of volume efficiency that becomes the highest values in different kinds of engine speed can be obtained and a high volume efficiency is obtained in a rotation speed range from low speed to high speed of an engine 12.